Mr Ganic is a former president of the Muslim-Croat Federation in Bosnia
A former member of Bosnia's wartime presidency has been held at Heathrow Airport over alleged war crimes.
Ejup Ganic, 63, was arrested in London after Serbia had issued an extradition warrant, the Metropolitan Police said.
He and 18 other officials are accused of conspiracy to murder 40 soldiers, in breach of the Geneva Convention.
Mr Ganic was later remanded in custody at Westminster Magistrates' Court. He is due to appear for another court hearing on 29 March.
The provisional extradition warrant relates to an attack on Yugoslav forces in Sarajevo at the beginning of the 1992-1995 Bosnian war.
Serbia claims more than 40 soldiers were killed in the so-called Dobrovoljacka Street attack, after Bosnia had declared independence from the Serb-led former Yugoslavia.
The soldiers were allegedly withdrawing from Sarajevo in a convoy at the time.
Mr Ganic, a professor at the University of Sarajevo, is one of 19 people for whom arrest warrants were issued in November and sent to Interpol.
Belgrade said it wanted to try Mr Ganic and other former Bosnian officials "in respect of conspiracy and the killing of wounded soldiers".
The Foreign Office confirmed the arrest, but said it was "inappropriate" to comment further as the case was now before the courts.
Serbia now has 45 days to provide full papers to the court supporting its extradition request.
The former leader served two separate terms as president of the Muslim-Croat Federation in Bosnia.
BBC diplomatic correspondent Bridget Kendall says the scars from the Bosnian conflict are still being felt 15 years on.
There is still a feeling in the different communities that they want to tell their stories, our correspondent says, and that the process of recognising that different people were victims has not ended.
Even though Europe had hoped this part of the world would enter a more stable relationship with itself and move towards joining the European community, there are still very deep wounds that have not healed, she adds.